LAUSR

BACKGROUND Pitching mechanics are believed to be risk factors for throwing elbow injury. Thus, a prospective study of abnormal mechanics in youth baseball players is needed. This study aimed to analyze the ulnar collateral ligament (UCL) during normal pitching using Software for Interactive Musculoskeletal Modeling (SIMM) for analysis, and investigate the risk parameters of throwing elbow injuries in youth baseball players. We hypothesized that excessive UCL force during pitching was a risk factor for throwing elbow injuries in this population. METHODS In this cohort study, youth baseball pitchers (aged 9-11 years) were instructed to throw a ball into a netted target. Using an SIMM musculoskeletal model, we analyzed the force of the anterior band of the anterior oblique ligament (AOL_AB), posterior band of the AOL (AOL_PB), and elbow varus moment during pitching (foot-contact to ball release). We calculated the integral of each force of the AOL_AB and AOL_PB during pitching, and summarized to establish an impulse at the medial epicondyle. Each participant was followed for 12 months to assess the occurrence of throwing elbow injury. RESULTS Eighteen pitchers (28.1%) reported throwing elbow injuries in the throwing arm during the 12-month follow-up period. The results of this study showed that the maximum AOL_PB force and the impulse at the medial epicondyle were risk factors for throwing elbow injuries. The maximum AOL_PB force was significantly higher in the throwing elbow injury group than in the uninjured group 59.4±17.8 N vs 47.1±17.5 N (P=0.014). The impulse at the medial epicondyle was also significantly different (11.1±4.0 N･s in the throwing elbow injury group versus 8.3±4.4 N･s in the uninjured group, P=0.025).results CONCLUSIONS: Increasing the AOL_PB force or the impulse at the medial epicondyle may increase the risk of throwing elbow injuries in youth baseball pitchers. It may be possible to reduce injury risk by focusing on ways to decrease AOL_PB load and cumulative stress on the medial epicondyle throughout the throwing motion, while still maintaining high levels of ball velocity.